X-rays have long been used to acquire images of the internal functioning of the patient's body for diagnostic purposes. More recently X-ray equipment has been used for assisting in invasive techniques such as biopsies and lithotripsy. For example, in X-ray mammography the breast of the patient is X-rayed and X-ray films are closely viewed to determine whether there are any microcalcification or other growths (hereinafter generally termed "lesions".) If a lesion is discovered then it is necessary to determine if it is a benign growth or if it requires immediate treatment. For such a determination is it often necessary to perform a biopsy to finally determine whether the lesion discovered in the X-ray image is pathological or benign. The radiologist performs a needle localization procedure whereby he inserts a radio opaque needle into the center of the susceptor growth to indicate to the surgeon the tissue to be excised. More particularly, the patient is brought to the mammographic system. The breast is compressed between horizontal plates attached to the X-ray equipment C-arm. The C-arm is a "C" shaped bracket which normally holds the X-ray tube at the top and the X-ray beam receptor at the bottom. The raiologist marks the breast or one of the compression plates at a point in a plane where he thinks the lesion is located, based on the study of the preliminary X-ray. An X-ray image is taken and developed to determine whether the marking is indeed in the correct location. If it is not in the correct location, then the radiologist repeats the marking procedure, acquiring another X-ray image. When the marking is indeed aligned with a lesion, the radiologist inserts the holder of the lesion-locating needle into the compressed breast through an aperture or recess in the compression plate at the marked point so as to center the holder tip within the lesion that was observed in the preliminary X-ray.
The breast is then removed from the compression plates and the C-arm is rotated 90 degrees, the breast is again compressed but now the compression plates are vertically aligned. Another X-ray is acquired to check the alignment of the needle holder tip and the lesion in the horizontal plane to assure that the holder tip is indeed within the lesion. If the holder tip is not within the lesion, or sufficiently close, the needle holder is moved and another image is acquired. The process is repeated until coincidence is obtained. Then the needle is inserted into the holder and the holder is withdrawn.
Thus in the prior art X-ray mammography a plurality of X-ray images and a plurality of breast clamping operations are required to position the needle holder to locate the lesion for the surgeon. The repeated operations are time consuming and uncomfortable for the patient and subject the patient to the X-ray dosage required to acquire the many images over a substantial area of the breast.
Radiologists and scientists have been seeking to improve the biopsy needle-positioning procedure. For example, the positioning procedure outlined hereinabove applies when the lesion can be seen in two orthogonal views. Sometimes the lesion can only be seen in one view. In March of 1984 a presentation at the National Conference on Breast Cancer of the American College of Radiation described a technique for a mammographic needle localization of lesions which cannot be imaged in two orthogonal views, but only in one of them. In this technique the X-ray beam is moved 30 degrees in a xeromammographic system where there is no breast clamping. An article describing the presentation appeared in the American Journal of Radiology Vol 144, pp 911-916, May 1985. The article describes a method that does not use C-arm clamping, and where by it is possible to locate the needle using images taken at two positions at 30 degrees apart.
Mammographic compression devices for normal X-ray film mammographic systems originally started with what may be described as dependent compression. At the top of the C-arm there was an X-ray tube and collimator arrangement which served as the source of the beam. A cone extended from the soruce to the breast to compress the breast against the X-ray radiation receptor or film at the bottom of C-arm. Thus the compression means i.e. the cone was fixedly attached to the C-arm. The movable film container provided the other side of the compression means. Rotating the C-arm also rotated the compression means.
Subsequently, movable compression plates were attached to the C-arm between the X-ray source at the top of the C-arm and the X-ray receptor (i.e. the film) at the other end. The movable compression plates were movably attached along the longitudinal axis of the C-arm to adjust to the woman's breast. In this arrangement the compression plates rotate with the C-arm. Thus, this arrangement also requires unclamping and reclamping the breast when the C-arm is rotated, even through small angles.
Compression plates are important in mammography to improve the quality of the image and to thereby enable the discovery of more lesions. When the breast is compressed it flattens and absorbs the X-ray beam less, and more uniformly. In addition extraneous movements are eliminated. These beneficial results of clamping improve the quality of the image. Therefore, it is highly desirable to compress the breast for mammographic breast image processing.
From the above description of the prior art it is readily understood that it would save time and reduce patient discomfort if a system could be provided that generates an immediate image to aid in positioning the lesion-locating needle holder for biopsy purposes. It would save further time and discomfort if it could utilize a single clamping position, and avoid movements of the lesion during reclamping with consequent relative movement of needle holder and lesion.
Until now, imaging chains have not been used for invasive mammographic techniques such as for positioning the biopsy locating needle. Until now the prior art systems using breast compression means have rotated the X-ray beam through 90 degrees for ascertaining that the needle holder tip is indeed within the lesion. The prior art systems have used an X-ray film means for acquiring images. When films are used as the X-ray receptor, waiting periods for the developing of the films are required before the radiologist can proceed with the next step in properly positioning the needle.
Accordingly, it is an object of the invention to provide mammographic biopsy needle positioning system using a radiographic imaging chain for providing the image which indicates the location of the needle holder.
It is also an object of the invention to provide in a system for positioning a biopsy needle locator in an X-ray mammographic system means for tilting the X-ray beam to obtain a parallax view of the needle holder and the breast without having to move the breast compression means when moving the beam. The system is designed to locate the biopsy needle in a minimum of time with a minimum of X-ray dosage and a maximum of accuracy.